A knocker-up was a profession in Britain and Ireland that started during and lasted well into the Industrial Revolution and at least as late as the 1920s before alarm clocks were affordable or reliable. A knocker-up's job was to rouse sleeping people so they could get to work on time.

The "knocker upper" was a common sight in Britain, particularly in the northern mill towns, where people worked shifts, or in London where dockers kept unusual hours, ruled as they were by the inconstant tides.

While the standard implement was a long fishing rod-like stick, other methods were employed, such as soft hammers, rattles and even pea shooters.

But who woke the knocker uppers? A tongue-twister from the time tackled this conundrum:

One problem knocker uppers faced was making sure workers did not get woken up for free.

"When knocking up began to be a regular trade, we used to rap or ring at the doors of our customers," Mrs Waters, a knocker upper in the north of England told an intrigued reporter from Canada's Huron Expositor newspaper in 1878.

"The public complained of being disturbed... by our loud rapping or ringing; and the knocker-up soon found out that while he knocked up one who paid him, he knocked up several on each side who did not," she continued.

The solution they hit on was modifying a long stick, with which to tap on the bedrooms windows of their clients, loudly enough to rouse those intended but softly enough not to disturb the rest.

The trade spread rapidly across the country, particularly in areas where poorly paid workers were required to work shifts but could not afford their own watches.